During operation of such apparatus as gas turbine engines, some of the components can experience damage such as might result from foreign objects impacting on the component, normal fatigue based on the cyclic life of the material from which the component is made, etc. In the higher temperature operating portions of such apparatus, there are included airfoil components such as turbine blades and vanes which are expensive to replace and sometimes costly to repair. For example, a crack occurring in such engine airfoils can generate surface oxides in the crack because of the high temperature operation under oxidizing conditions.
In the case of nickel-base superalloys which include the element Al and generally the element Ti, the creation of complex oxides including one or both of Al and Ti along with other elements of the superalloy from which such article is made, presents a difficult crack healing problem: the oxide must be removed in order to repair satisfactorily the crevice or crack. Such oxides are impractical to remove solely through exposure to a reducing atmosphere without exposing the superalloy article to temperatures detrimental to its mechanical properties or to its structural integrity. Therefore, such repairs have sometimes been made by benching out or cutting away and replacing the damaged portion of the component.